This invention relates to a process for the production of dichloroisobutenes, namely cis- and trans-1,3-dichloro-2-methylpropene and 3-chloro-2-chloromethylpropene.
Among the aforementioned products, 3-chloro-2-chloromethyl-propene, in particular, is of interest as an intermediate for a number of organic syntheses, i.e., for the syntheses of crown ethers (C. A. 90 (1979), p. 644, 90: 121561 a; C. A. 93 (1980), p. 697, 93: 204708 s) while cis- and trans-1,3-dichloro-2-methyl-propenes are used as molecular weight controllers in a polymerization reaction, or nematocides (C. A. 77 (1972), p. 22, 75779 j; molecular weight controller; C. A. 93, (1980), p. 192, 93: 127082 d, nematocides) and also utilized for further chlorination.
According to East German Pat. No. 106,345, the aforementioned dichloroisobutenes can be manufactured by the gas-phase chlorination of isobutene at 60.degree.-80.degree. C. Using an isobutene/chlorine ratio of 0.4 to 0.5, there is obtained about 30% of 1,3-dichloro-2-methylpropene, 30% of 3-chloro-2-chloromethylpropene, 30% of 1,2,3-trichloro-2-methyl-propane, and 10% of 3-chloro-2-methylpropene.
In other known manufacturing methods, 3-chloro-2-methylpropene is further chlorinated with chlorine at low temperatures. Under controlled conditions, there is obtained about 25-30% of 3-chloro-2-chloromethylpropene, 25% of 1,3-dichloro-2-methylpropene, 30% of 1,2,3-trichloro-2-methylpropane, together with other higher-chlorinated products (Z. Chem. 8 [1968 ]6: 220-221; J. Am. Chem. Soc. 69: 2 614-2 616 [1947]; and Chem. Abstr. 63: 4 148 [1965]).
The further chlorination of 3-chloro-2-methylpropene with SO.sub.2 Cl.sub.2 is reported to give an 83% yield of 1,2,3-trichloro-2-methylpropane (J. Am. Chem. Soc. 68: 787 [1946]).
These prior art processes for the production of dichloroisobutenes generally give rise to appreciable quantities of undesired by-products.